From the technical perspective, the functionality of the XMLHttpRequest is very common and basic in the Swing framework. In Swing you can invoke asynchronously methods in a convenient way, using the SwingUtilities class. Field validation, auto completion, powerful tables, drag and drop are very easy to implement. Swing is even more powerful. Just try out the aerith application.The look and feel of aerith is really cool and from my point of view more exciting than XMLHttpObject. Even more exciting is the LookingGlass Java 3D desktop. You can build 3d applications in Java - a great extension to a media center.
From the architectural perspective: XMLHttpRequest can improve the usability of web applications. Users can become even more productive. Auto-completion, validation and asynchronous requests are an enrichment of existing applications. BUT: AJAX will remain a hack, because this technology only provides already exisitng functionality for browser environment with additional effort.
Why we should spend more time, to reinvent the wheel? This question is quite interesting and can be answered considering the non functional requirement. For internet applications, it is much easier to deploy AJAX, instead of Java or .NET. But in intranet environments, JavaWebStart can be used to deploy a Swing app. Swing provides more functionality, than AJAX, with less implementation overhead.
For internet applications also Applets can be used to provide rich experience to the user. In the past, also applets had problems with compatibility (JDBC and RMI were not supported in the IE). But now Applets are more compatible, than "AJAX". You only need the JRE, which takes about 18 MB.
I suppose we have to wait, until Applets will be renamed into another, cool name like Richlets or I-Lets :-).
In real world project, it is very important to choose the right technology. There are no silver bullets... The architect has to decide between the technology considering the functional, and non-functional requirements.
Considering the past, hyping a technology is a not always a very good idea...
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